/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 * Copyright 2021 OmniOS Community Edition (OmniOSce) Association.
 */

#include <sys/copyops.h>
#include <sys/errno.h>
#include <sys/kmem.h>
#include <sys/param.h>
#include <sys/pathname.h>
#include <sys/sysmacros.h>
#include <sys/systm.h>
#include <sys/types.h>
#include <sys/vnode.h>

int
getcwd(char *buf, size_t buflen)
{
        int err;
        char *kbuf;
        size_t kbuflen;

        /*
         * If the buffer cannot accommodate one character and nul terminator,
         * it is too small.
         */
        if (buflen < 2)
                return (set_errno(ERANGE));

        /*
         * The user should be able to specify any size buffer, but we don't want
         * to arbitrarily allocate huge kernel buffers just because the user
         * requests it.  So we'll start with MAXPATHLEN (which should hold any
         * normal path), and only increase it if we fail with
         * ERANGE / ENAMETOOLONG.
         *
         * To protect against unbounded memory usage, cap to kmem_max_cached.
         * This is far bigger than the length of any practical path on the
         * system, and avoids allocating memory from the kmem_oversized arena.
         */
        kbuflen = MIN(buflen, MAXPATHLEN);

        while (kbuflen <= kmem_max_cached) {
                kbuf = kmem_alloc(kbuflen, KM_SLEEP);

                if (((err = dogetcwd(kbuf, kbuflen)) == 0) &&
                    (copyout(kbuf, buf, strlen(kbuf) + 1) != 0)) {
                        err = EFAULT;
                }

                kmem_free(kbuf, kbuflen);

                /*
                 * dogetcwd() inconsistently returns ERANGE or ENAMETOOLONG
                 * depending on whether it calls dirtopath() and then whether
                 * the subsequent operations run out of space whilst
                 * evaluating a cached vnode path or otherwise.
                 */
                if (err == ENAMETOOLONG || err == ERANGE) {
                        /* For some reason, getcwd() uses ERANGE. */
                        err = ERANGE;
                        /*
                         * If the user's buffer really was too small, give up.
                         */
                        if (kbuflen == buflen)
                                break;
                        kbuflen = MIN(kbuflen * 2, buflen);
                } else {
                        break;
                }
        }

        return ((err != 0) ? set_errno(err) : 0);
}